In production of semiconductor integrated circuit boards, in the process of forming a circuit with a metal such as copper on a surface of a silicon wafer, unevenness or steps are generated on a surface of the silicon wafer, and therefore generally a metallic portion of the circuit is at first removed by polishing to eliminate steps on the surface. When an aluminum wiring is formed on a silicon wafer and a film of oxide such as silica is provided on the aluminum wiring as an insulating film, unevenness is generated due to the wiring, and therefore the oxide film is polished for flattening. In the process of polishing the circuit board, it is required that there is no step nor unevenness on the polished surface, the surface is flat and smooth without any flaw at the micro level, and also that the polishing rate is high.
Furthermore, in the field of semiconductor materials, a degree of integration has been becoming increasingly higher in association with the tendency for downsizing and higher sophistication in performance of electric and electronic products, and if there are impurities such as Na or K, for instance, in a transistor separation layer, sometimes the expected performance is not provided, or a failure may occur. Especially, when Na is deposited on a surface of a polished semiconductor substrate or an oxide film, because dispersibility of Na is high, Na is captured in blemishes or the like of the oxide film, which in turn may cause insulating fault or short circuitry when a circuit is formed on the semiconductor substrate, or may cause lowering of the dielectric constant. Because of the features as described above, or when the semiconductor substrate is used for a long time, a failure may occur. Therefore, particles for polishing including little impurities such as Na or K are strongly required.
A silica sol, fumed silica, fumed alumina or the like have been used as particles for polishing.
Polishing agents used in the CMP (Chemical Mechanical Polishing) process generally comprises spherical particles for polishing formed with a metal oxide such as silica or alumina with the average particle diameter of around 200 nm, an oxidant for the purpose to improve the polishing rate for metals for metals for wiring or circuits, and an additive such as an organic acid, and a solvent such as pure water. Because steps (convex and concave sections) caused by a groove pattern for wiring formed on the base insulating film are present on a surface of a polished material (substrate), and therefore it is required to polish the substrate down to the common plane mainly removing the convex sections for obtaining a flat surface. With the conventional spherical particles for polishing, however, when a portion above the common plane is polished, sometimes metal for circuitry within a wiring groove under a concave section may disadvantageously be polished even to a level lower than the common plane (this problem is referred to as “dishing”). When the dishing occurs, a thickness of wiring may become smaller to cause various problems such as increase of wiring resistance or lowering of flatness of an insulating film formed on the portion. Therefore it is required to suppress occurrence of dishing.
It is known that, when a polishing agent including particles having peculiar forms is used for polishing a substrate having the unevenness (convex and concave sections) as described above, polishing of the concave sections is suppressed until upper end faces of the convex sections are polished to the same level of bottom faces of the concave sections, and that, after the upper faces of the convex sections are polished down to the bottom faces of the concave sections, both the convex and concave sections are polished at the same polishing rate, and therefore dishing does not occur, and the polished surface of the substrate does not have the unevenness and is excellent in the flatness. With the polishing agent, dishing does not occur in a polishing process for forming, for instance, a semiconductor integrated circuit, and therefore increase of circuit resistance in the obtained integrated circuit does not occur, and a surface of the polishing substrate is excellent in the flatness, so that a laminated integrated circuit can efficiently be formed.
Expected fields for application of the polishing agent including particles having peculiar forms aluminum include mirror finish of wiring on an aluminum disk (aluminum or a metal skin of aluminum substrate) or on a semiconductor multi-layered wiring substrate, a glass substrate of an optical disk or a magnetic disk, a glass substrate of a liquid crystal display, a glass substrate of a photo mask, and other vitreous materials.
JP H01-317115A (Patent document 1) discloses a method of producing a silica sol including heteromorphic particles of silica with the ratio D1/D2 of more than 5 wherein D1 indicates a particle diameter measured by the image analysis method and is in the range from 40 to 500 millimicrons, and D2 indicates a particle diameter measured by the nitrogen gas adsorption method. The silica sol produced by the method of the present invention includes amorphous colloidal silica particles extending in one plain with homogeneous diameter in the range of 5 to 40 millimicrons observed by an electron microscope to make elongate shape dispersed in liquid medium. The method comprises the steps of: (a) adding a predefined volume of an aqueous solution containing water-soluble calcium salt, magnesium salt or the like in a predefined colloidal aqueous solution of activated silicic acid and agitating the mixture solution; (b) adding an alkali metal oxide, a water-soluble organic base, or a water-soluble silicate of the compounds is added so as to make the mole ratio of SiO2/M2O to be in the range of 20 to 200 (M indicates a molecule of the alkali metal oxide or the organic base); and (c) heating the mixture in the step at 60-150 degrees C. for 0.5-40 hours.
JP H04-65314A (Patent document 2) describes a method of producing a stable silica sol with the SiO2 concentration of 50% by weight or below and the ratio D1/D2 in the range from 3 to 5 wherein D1 indicates a particle diameter measured by the image analysis method and is in the range from 40 to 500 millimicrons, and D2 indicates a particle diameter measured by the nitrogen gas adsorption method. In the method, when addition of an aqueous solution of the active silicic acid to a sol of slender silica particles, collapse of colloidal silica particles in the feed sol does not occur, and the added active silicic acid is deposited via the siloxane bond on a surface of the original slender particle to provide colloidal silica having a slender form with the diameter increased from the original one.
JP H04-187512A (Patent document 3) discloses a method of producing a sol, in which chain-like silica particles are dispersed in a solvent, with the SiO2/M2O molar ratio in the range from 60 to 100. This method comprises the steps of adding a silicic acid solution into an aqueous solution of an alkali metal silicate with the SiO2 content in the range from 0.05 to 5.0% by weight to prepare a mixture solution with the SiO2/M2O ratio in the range from 30 to 60; adding a compound of one or more types of metals selected from the group consisting of Ca, Mg, Al, In, Ti, Zr, Sn, Si, Sb, Fe, Cu, and rare earth metals (before, during, or after addition of the silicic acid solution) to the mixture solution; maintaining the mixture solution at a temperature of 60 degrees C. or more for a prespecified period of time; and further adding a silicic acid solution into the mixture solution.
JP 3441142C (Patent document 4) proposes a polishing agent for semiconductor wafers comprising a stable silica sol in which a percentage of a silica particles having a major axis in the range from 7 to 1000 nm and a minor axis/major axis ratio in the range from 0.3 to 0.8 is 50% or more among all of the particles contained in the sol.
JP H07-118008A (Patent document 5) discloses a method of producing a sol of slender silica particles, and the method comprises the steps of adding an aqueous solution of a water-soluble potassium salt, a water-soluble magnesium salt, or a mixture thereof into a colloidal solution of active silicic acid; adding an alkaline substance into the obtained aqueous solution; heating a portion of the obtained mixture material up to 60 degrees C. or more to prepare a heel liquid (with the remaining portion defined as a feed liquid herein); adding the heel liquid to the feed liquid to evaporate water during the adding operation for obtaining a condensed liquid with the SiO2 concentration in the range from 6 to 30% by weight.
JP H08-279480A (Patent document 6) discloses that, in the aqueous solution of colloidal silica prepared by, for instance, (1) a method in which an aqueous solution of alkali silicate is neutralized with a mineral acid, an alkaline substance is added in the neutralized solution, and the mixture solution is heated for aging; (2) a method in which an alkaline substance is added in active silicic acid obtained by subjecting an aqueous solution of alkali silicate to positive ion exchange, and the mixture solution is heated for aging; (3) a method in which active silicic acid obtained by hydrolyzing alkoxy silane such as ethyl silicate is heated for aging; and (4) a method in which silica particles are directly dispersed in an aqueous medium, colloidal silica generally having the diameter in the range from 4 to 1,000 nanometers and preferably having the diameter in the range from 7 to 500 nanometers are dispersed in an aqueous medium, and that the colloidal silica aqueous solution has the concentration in the range from 0.5 to 50% by weight and preferably in the range from 0.5 to 30% by weight calculated as that of SiO2. The document also describes that forms of the silica particles include a spherical form, irregular form, a flat form, a plate-like form, a slender form, a fibrous form, and the like.
JP H11-214338A (Patent document 7) discloses a method of polishing a silicon wafer with a polishing agent containing colloidal silica particles as the main component, and the colloidal silica particles are obtained by methyl silicate refined by distillation is reacted to water in a methanol solvent in the presence of ammonia or in the presence of ammonia and ammonium salt as catalysts, and the major axis/minor axis ratio of the colloidal silica particle is 1.4 or more.
WO 00-15552A (Patent document 8) discloses a silica sol comprising spherical colloidal silica particles with the average diameter in the range from 10 to 80 nanometers and silica containing a metal oxide and bonding the spherical colloidal silica particles to each other, in which the ratio D1/D2 of the particle diameter (D1) measured by the image analysis method versus the average diameter of the spherical colloidal silica particles (D2: measured by the nitrogen adsorption method) is 3 or more, D1 is in the range from 50 to 500 nanometers, and the spherical colloidal silica particles are coupled to each other on one plain to form beads-like colloidal silica particles.
Patent document 8 also describes a method of producing the silica sol, and the method comprises the steps of (a) adding an aqueous solution of water-soluble metal salt to a predefined amount of a colloid aqueous solution of active silicic acid or an acidic silica sol so that a content of a metal oxide in the mixture solution against SiO2 in the colloid aqueous solution or in the acidic silica sol is in the range from 1 to 10% by weight to prepare a mixture solution 1; (b) adding an acidic sol of spherical silica particles with the average diameter in the range from 10 to 80 nanometers and with the pH in the range from 2 to 6 to the mixture solution 1 so that the weight ratio A/B (A indicating a content of silica originated from the acidic sol of spherical silica particles and B indicating a content of silica originated from the mixture solution 1) is in the range from 5 to 100, and at the same time so that a total content (A+B) of silica in a mixture solution 2 obtained by mixing the acidic sol of spherical silica particles with the mixture solution 1 is in the range from 5 to 50% by weight of SiO2 in the mixture solution 2; and (c) adding, a hydroxide of alkali metal, a water-soluble organic base or a water-soluble silicate salt the obtained mixture solution 2 so that the pH is in the range from 7 to 11, and heating the resultant mixture solution.
JP 2001-11433A (Patent document 9) describes a method of producing a sol of beads-like silica particles, and the method comprises the steps of an aqueous solution containing a water-soluble salt of bivalent or trivalent metal singly or in combination with salt(s) of other metal(s) in a colloid aqueous solution of active silicic acid containing SiO2 by 0.5 to 10% by weight and also having pH of 2 to 6 so that a content of the metal oxide (calculated as that of MO in a case of a salt of a bivalent metal, and of M2O3 in a case of a trivalent metal, and M indicating a bivalent or trivalent metal atom, and O indicating an oxygen atom) against SiO2 in the colloid aqueous solution of the active silicic acid and agitating the obtained mixture solution to obtain a mixture solution (1); adding an acidic sol of spherical silica particles with the average diameter in the range from 10 to 120 nm and also having the pH of 2 to 6 in the obtained mixture solution (1) so that a ratio A/B (weight ratio) of a content of silica originated from the acidic sol of spherical silica particles (A) and a content of silica originated from the mixture solution (1) (B) is in the range from 5 to 100, and at the same time so that a total content of silica (A+B) in a mixture solution (2) obtained by adding the acidic sol of spherical silica with the mixture solution (1) is in the range from 5 to 40% by weight calculated as that of SiO2 in the mixture solution (2) and agitating the resultant mixture solution; adding a hydroxide of alkali metal or the like in the mixture solution (2) so that the pH is in the range from 7 to 11 to obtain a mixture solution (3); and heating the obtained mixture solution (3) at a temperature in the range from 100 to 200 degrees C. for 0.5 to 50 hours to obtain a sol of beads-like silica.
JP 2001-48520A (Patent document 10) discloses a method of producing a silica sol in which amorphous silica particles with the average diameter in the range from 5 to 100 nanometers when observed with an electron microscope in the diametrical direction and the length in the range from 1.5 to 50 times of the diameter and also having a slender form are dispersed in a liquid-like dispersing medium. The method comprises the steps of hydrolyzing alkyl silicate with an acid catalyst without using a solvent in a composition with the silica concentration of 1 to 8 mole/litter, the acid concentration of 0.0018 to 0.18 mole/litter, and the water concentration of 0.2 to 1.5 mole/litters; then diluting the hydrolyte with water so that the silica concentration is in the range from 0.2 to 1.5 mole/litter; adding an alkaline catalyst so that the pH is 7 or more; and heating the solution to proceed polymerization of the silicic acid.
JP 2001-150334A (Patent document 11) discloses a method of producing a sol of silica particles each having a distorted form, and the method comprises the steps of adding an alkali-earth metal such as salts of Ca, Mg, and Ba to an acidic aqueous solution of active silicic acid with the SiO2 concentration of 2 to 6% by weight obtained by subjecting an aqueous solution of an alkali metal silicate such as water glass to the processing for removing positive ions at a weight ratio of 100 to 1500 ppm against SiO2 contained in the active silicic acid calculated as that of the oxide; furthermore adding the alkaline substance to the solution obtained in the step above so that the SiO2/M2O ratio (M denoting an alkali metal atom, NH4 or a quaternary ammonium group) is in the range from 20 to 150 to obtain an original heel liquid; repeating the same step to obtain, as a charge liquid, an aqueous solution of active silicic acid having the SiO2/M2O molar ratio (M denoting an alkali metal atom, NH4 or a quaternary ammonium group) in the range from 20 to 150 calculated based on the SiO2 concentration with the concentration of 2 to 6% by weight; and evaporating and removing water from the solution at a rate of 0.05 to 1.0 calculated as the weight ratio of SiO2 in the charge liquid/SiO2 in the original heel liquid per hour (this final step may optionally be eliminated).
JP 2003-133267A (Patent document 12) describes that the particles for polishing containing groups of particles having irregular forms in which two or more primary particles having the average diameter in the range from 5 to 300 nanometers are coupled to each other, especially particles for polishing in which a percentage of the primary particles constituting the groups of irregularly-formed particles against the total number of primary particles in the particles for polishing is in the range from 5 to 100% are effective as particles for polishing capable of being applied to polishing a surface of a substrate for flattening without causing dishing (excessive abrasion).
JP 2004-288732A (Patent document 13) discloses a slurry for polishing a semiconductor substrate containing non-spherical colloidal silica, an oxidizing agent, and an organic acid, and water in which a major axis/minor axis ratio of the non-spherical colloidal silica is in the range from 1.2 to 5.0, while also JP 2004-311652A (Patent document 14) discloses similar non-spherical colloidal silica.
JP H10-128121A (Patent document 15) describes a method of producing a silica sol or a composite silica sol in which an aqueous solution of an alkali silicate is added, in the presence of an electrolyte, to a dispersion liquid of core particles or an aqueous solution of an alkali silicate to grow core particles to produce a silica sol, or in which an aqueous solution of an alkali silicate and an aqueous solution of a metal salt other than silicate or an aqueous solution of a non-metal salt is added, in the presence of an electrolyte, to an aqueous solution of core particles or an aqueous solution of an alkali silicate to grow core particles to produce a sol of silica-based composite oxide particles. According to the document, in the production method, the production efficiency is excellent and a particle growth rate is high, and therefore the method makes it possible to obtain a stable sol of silica particles or silica-based composite oxide particles with homogeneous diameters.
The present applicant proposed, in JP 2003-26417A (Patent document 16), a method of producing a stable sol of silica particles having homogeneous particle diameters, in which the production efficiency is excellent and a rage of particle growth rate is high. In this method, a liquid II (an aqueous solution of an alkali silicate) is added, in the presence of an electrolyte comprising a strong acid, to a liquid I (a dispersion liquid of core particles or an aqueous solution of an alkali silicate) to grow core particles so that the equivalent ratio (EA/EE) (EA indicating a chemical equivalent of alkali in the liquid II and EE indicating a chemical equivalent of electrolyte) is set to the range from 0.5 to 8.
With the production method, it is possible to obtain a stable sol of silica particles having homogeneous particle diameters, but when the sol is used as a composition for polishing, the polishing performance is limited.
JP H03-257010A (Patent document 17) describes an example of silica-based particles each having projections on a surface thereof, and the silica particles have, on a surface thereof, successive irregular projections each having the size in the range from 0.2 to 5 μm when observed with an electron microscope, the average diameter in the range from 5 to 100 μm, the specific surface area of 20 m2/g or below when measured by the BET method, and the pore volume of 0.1 mL/g or below.
JP 2002-38049A (Patent document 18) describes silica-based particles each having a substantially spherical and/or semi-spherical projections on an entire surface of the core particle in which the projections are bonded to the core particles by chemical bond, and also describes silica-based particles each having a substantially spherical and/or semi-spherical projections on an entire surface of the core particle in which the projections are chemically bonded to the core particles. Furthermore, the document describes a method of producing silica-based particles, and the method comprises the steps of (A) generating polyorgano-siloxane by hydrolyzing a specific alkoxysilane compound and condensating the hydrolyte, (B) subjecting the polyorgano-siloxane particles to the surface processing with a surface absorbent; and (C) forming projections on the entire surface of the polyorgano-siloxane particle having been subjected to the surface processing in step (B) above with the alkoxysilane compound.
JP 2004-35293A (Patent document 19) discloses silica-based particles each having substantially spherical or semi-spherical particles on the entire surface of a maternal particle thereof. The silica-based particle is characterized in that the projections are chemically bonded to the maternal particles, and a compressive elasticity modulus of the material particle when compressed by 10% is different from that of the projection.
However, the articles described in JP H03-257010A (Patent document 17) are mainly those having the average diameter in the range from 5 to 10 μm, and the silica-based particles disclosed in JP 2002-38049A (Patent document 18) are only those with the average diameter substantially in the range from 0.5 to 30 μm, and what is described above is also applicable to JP 2004-35293A (Patent document 19).
The present applicant reports, in JP 2001-352966A (Patent document 20), in relation to the technique for promoting aggregation or deposition of materials present in a liquid by adding a silica sol to a prespecified liquid, a lee-depositing agent for fermented liquid foods, and reports in the document that the agent is a sol in which silica particles are dispersed in water and a zeta potential of the particles is a negative value and the absolute value is 35 mV or more when the pH of the sol is in the range from 4 to 6, and also that, when the sol was added to soy sauce, then after 3 hours, turbidity of the soy sauce lowered from 58 to 20.    [Patent document 1] JP H01-317115A    [Patent document 2] JP H04-65314A    [Patent document 3] JP H04-187512A    [Patent document 4] JP 3441142C    [Patent document 5] JP H07-118008A    [Patent document 6] JP H08-279480A    [Patent document 7] JP H1-214338A    [Patent document 8] WO 00-15552A    [Patent document 9] JP 2001-11433A    [Patent document 10] JP 2001-48520A    [Patent document 11] JP 2001-150334A    [Patent document 12] JP2003-133267A    [Patent document 13] JP 2004-288732A    [Patent document 14] JP 2004-311652A    [Patent document 15] JP H10-128121A    [Patent document 16] JP 2003-26417A    [Patent document 17] JP H03-257010A    [Patent document 18] JP 2002-38049A    [Patent document 19] JP 2004-35293A    [Patent document 20] JP 2001-352966A